[phenixbb] protein-ligand complex structure

Wei Shi wei.shi118 at gmail.com
Thu Oct 24 19:19:04 PDT 2013

Hi all,
I am working on a structure of protein-ligand complex. Four ligands are
placed for the dimer protein and the density for the two ligands of the
first monomer is better than the density for the other two ligands of the
second monomer. Ligand is moved to fit density better in Coot (and for two
ligands of the first monomer, they fits the density almost perfectly), but
after a refinement in phenix (default settings + NCS restraints + Secondary
structural restraints + Optimize X-ray/stereochemistry weight +Optimize
X-ray/ADP weight), some part of the ligand which fits density good before
moved out of the density again...Besides, it always shows green density in
Coot for the ligand region even in places where the ligand is in density...
Any suggestions or ideas about how to fit the ligand better and why the
density for ligands of the second monomer is worse than that for the first
monomer and why the ligands would move out of density after refinement?
Is it because the protein model is not good enough to get the ligand
density good? There is a conformational change upon ligand binding, and I
rebuilt some part of the protein manually, and the density for a region of
about 30 residues is not very good, and I tried to mutate those to alanies
and refine, but it didn't help me see the density better...
Any suggestions or ideas on how to improve this protein-complex structural
model?  Thank you so much!
The statistics for the current best model is as follows, and the resolution
of the dataset is 2.8Å.

                           start         final
  R-work:           0.3359        0.2993
  R-free:             0.3619        0.3558
  RMS(angles):     1.03           1.55
  RMS(bonds):    0.006          0.007

MolProbity validation
Ramachandran outliers:   4.7% (Goal: < 0.2%)
Ramachandran favored:  85.3% (Goal: > 98%)
Rotamer outliers:   4.5% (Goal: 1%)
C-beta outliers:   0    (Goal: 0)
Clashscore:   7.43
Overall score:   2.56

Thank you so much!

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